I'm experimenting with a schematic of an audio amp in LTspice. First I looked at the DC bias currents of the amp with the ".op directive". The results showed bias currents:

IC(Q2) = 0.929 mA

I(R2) = 0.916 mA

IB(Q4) = 0.0125 mA

IC(Q4) = 4.83 mA

This Spice result for I(R13) (base current going to Q4) is lower than my own calculations.

First I calculated the intrinsic emitter resistance of Q4:

re = Vt / IC(Q4) = 26mV/4.83mA = 5.41 ohm.

Then i drawed the schematic to determine the equivalent resistance that the collector of Q2 sees (in the red highlighted area).

The input resistance of Q4 is:

Beta(Q4) * re = 294.3 *5.41 ohm = 1.59K (I looked up the current gain in the model parameters of the BC546B, BF=294.3)

This resistance is in series with R13 --> 4.7K + 1.59K = 6.29K

The current into the base of Q4 can be calculated with the current division rule:

IB(Q4) = 800 / (800 + 6.29K) * IC(Q2) = 0.11 * 0.929 mA = 0.102 mA

As you can see this does not match with the Spice result (IB(Q4) = 0.0125 mA).

Has anyone an idea if my calculations are correct?